Optical coupling into and out of waveguides in photonic integrated structures can have reduced efficiencies due to light leaking out of the waveguides at the edge of the structure interacting with oxides encapsulating the waveguide, as well as insulator layers between the waveguide and a substrate. The losses occur mainly due to differences in indices of refraction between the waveguide, the insulator layers and the encapsulating oxides; the losses can be particularly acute when silicon substrates are used.